1. Field of the Invention
This invention relates to a lens device and a correction method for the lens device.
2. Description of the Related Art
There has been a progress in lens performance, and thus there has been a demand for lens position adjustment at a level which cannot be supported in conventional lens processing and adjustment. In particular, in a lens having performance superior to that of a high-definition television broadcast system, an effect of the adjustment is significant. For example, on the basis of respective functions, box-type lenses can be classified into five parts of a focus lens group, a zoom lens group, a vibration-proof lens group, an extender, and a master lens group. In a theoretical lens shape and mechanical components, focal positions at zoom positions are predetermined. However, the focal position is shifted due to an abnormal state caused by a lens surface shape, processing errors in mechanical dimensions, and the like, and thus a phenomenon, in which a focal position is minutely shifted in accordance with the zoom position, occurs (zooming focus shift). Further, also in a diaphragm which is disposed behind the zoom lens group, a phenomenon, in which the focal position is shifted, occurs (stopping focus shift).
In the conventional art, such a change has been dealt with by selection of mechanical components or the like. However, the conventional art is unable to achieve performance superior to that of a high-definition television broadcast system, and thus it is not possible to obtain desired performance.
Hence, there is a lens in which on the basis of the correspondence relationship between the zoom positions and the focal positions, a position of a focus lens is adjusted in accordance with the zoom position (JP2004-233892A). Further, there is a lens in which a focal position is corrected in accordance with the zoom position (JP2003-57528A), and also there is a lens in which correction is performed on only a master lens group (JP1998-186209A (JP-H10-186209A)).